1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device. In particular, the present invention relates to an annealing process that activates conductive impurities doped in a silicon carbide substrate.
2. Description of the Related Art
Many semiconductor devices that utilize silicon carbide in a substrate material have been developed. In manufacturing a semiconductor device that utilizes a silicon carbide substrate, an annealing process in which the silicon carbide substrate is heated to a high temperature close to 2000 degrees Celsius is performed in order to activate the conductive impurities that have been doped. In this type of high temperature annealing process, the silicon carbide substrate may be damaged. That is, the following problems may readily occur: silicon atoms or conductive impurities may depart from the surface of the silicon carbide substrate to the exterior, thereby damaging the surface of the silicon carbide substrate or reducing the concentration of impurities in its surface layer part.
In order to deal with this problem, Japanese Patent Application Publication No. 2001-68428 teaches a technique in which a surface of a silicon carbide substrate is covered by a cap layer prior to an annealing process. In this technique, the cap layer is formed from DLC (diamond like carbon). According to Patent Document 1, with the cap layer that is formed from DLC, hydrogen atoms or oxygen atoms that leave during the annealing process are graphitized. The melting point of graphite exceeds 3000 degrees Celsius. As a result, in cases where the cap layer is formed from DLC, the surface of the silicon carbide substrate is reliably protected even if the annealing process is performed at a high temperature close to 2000 degrees Celsius.